This invention relates to tank-type electric motor-operated vacuum cleaners, and more particularly relates to a collapsible frame for limiting downstream movement of the primary or upstream filter in a two element air filtering system of a so-called wet/dry vacuum cleaner.
In many tank type wet/dry vacuum cleaners a cage which extends into the dirt receiving cannister is often provided as a support for a tubular air filter element or a wrap of air filtering material. Such a construction is illustrated in U.S. Pat. No. 4,185,974, issued Jan. 29, 1980 to K. R. Hrister, for an "Integral Filter Cage and Lid For Cannister Type Vacuum Cleaner". While a single air filter of this type is sufficient for most operating conditions, under severe conditions the limited filtering area results in clogging of the filter after only a short period of operation so that it must be cleaned or changed very often. To extend the operating period between filter cleaning and/or replacement and also to improve air cleaning, the prior art approach has been to add a second relatively large filter that is constituted by a blanket of porous material inserted into the dirt accumulating tank. In order to prevent the added or primary filter from being drawn into contact with the original or secondary filter and blocking air flow thereto, the prior art has also provided a second filter cage that is interposed between the primary and secondary filters.
In prior art constructions, the size and shape of the second cage has been such that it is necessary to dismount same in order to gain access to the first filter for replacement or cleaning thereof.
In one prior art construction, the second filter cage is placed into the primary filter blanket after the latter has been placed over in the tank opening. The lid is then placed over the second cage, primary filter and tank. This construction has the disadvantage of causing the user to remove the second cage each time the tank is emptied, and since the second cage is not attached, it is subject to loss and damage when separated from the unit.
In another prior art construction, the second cage is snap connected to the lid and is removed by using enough force to overcome the resilience of the snaps. This construction has the advantage of staying attached to the lid when the tank is being emptied. However, it must be removed from the lid to change or clean the secondary filter. But, once removed, it has the same disadvantage listed above. In a further prior art construction, the second cage is attached to the lid with screws or the like. Obviously, this is the least desirable since the second cage must be separated from the unit to gain access to the secondary filter and tools are required for such operation.